Lifting mast for an industrial truck

Abstract

The invention relates to a lifting mast (10) for a material handling vehicle (1a), in particular a double-stacker (1), wherein the lifting mast (10) has an outer mast (15) designed as a stationary mast and an inner mast (16) arranged in the outer mast (15) so as to be raised and lowered, wherein a load carriage (11) provided with two fork arms (12a, 12b) is arranged in the inner mast (16) so as to be raised and lowered, wherein the outer mast (15) is formed by two laterally spaced vertical outer mast profiles (15a, 15b) and the inner mast (16) is formed by two laterally spaced vertical inner mast profiles (16a, 16b), wherein a mast lifting cylinder device (20) is provided which is designed to raise and lower the inner mast (16) in the outer mast (15), and a free lifting cylinder device (21) is designed to raise and lower the load carriage (11) in the inner mast (16).The mast lifting cylinder assembly (20) comprises a single mast lifting cylinder (20a) and the free lifting cylinder assembly (21) comprises a single free lifting cylinder (21a), wherein the mast lifting cylinder (20a) and the free lifting cylinder (21a) are arranged side by side in a central area (MB) of the lifting mast (10) between the two vertical inner mast profiles (16a, 16b).

Description

[0001] The invention relates to a lifting mast for a forklift truck, in particular a double-stacker, wherein the lifting mast has an outer mast designed as a stationary mast and an inner mast arranged in the outer mast in a way that can be raised and lowered, wherein a load carriage equipped with two fork arms is arranged in the inner mast in a way that can be raised and lowered, wherein the outer mast is formed by two laterally spaced vertical outer mast profiles and the inner mast is formed by two laterally spaced vertical inner mast profiles, wherein a mast lifting cylinder device is provided which is designed to raise and lower the inner mast in the outer mast, and a free lifting cylinder device is provided which is designed to raise and lower the load carriage in the inner mast.

[0002] Double-stacker pallet trucks are used especially for loading and unloading trucks.

[0003] For this application, small external dimensions of the double-stacker pallet truck, in particular a small vehicle width and a small vehicle length, are essential requirements in order to make the loading and unloading of trucks as efficient as possible and to achieve increased maneuverability in order to optimize warehouse utilization.

[0004] In known double-stacker pallet trucks, the lifting mast for the inner mast stroke has a mast lift cylinder assembly within the outer mast. This assembly consists of two mast lift cylinders located on the outer sides of the two vertical outer mast profiles. Protective devices are required for these cylinders to prevent mechanical damage during operation. A separate free-lift cylinder is provided for the free lift of the load carriage within the inner mast. The lifting mast of a known double-stacker pallet truck thus has a total of three lift cylinders, resulting in a complex design and high oil consumption. Consequently, a correspondingly large oil tank for the hydraulic pump unit must be provided within the pallet truck.

[0005] The present invention is based on the objective of providing a lifting mast that is improved with regard to the aforementioned disadvantages.

[0006] This problem is solved according to the invention by the fact that the mast lifting cylinder device comprises a single mast lifting cylinder and the free lifting cylinder device comprises a single free lifting cylinder, wherein the mast lifting cylinder and the free lifting cylinder are arranged laterally next to each other in a central area of ​​the lifting mast between the two vertical inner mast profiles.

[0007] According to the invention, the lifting mast thus comprises a single mast lift cylinder and a single free lift cylinder, so that the lifting mast has a total of only two lift cylinders, one for the mast lift and one for the free lift. The mast lift cylinder and the free lift cylinder are arranged laterally next to each other, i.e., adjacent and adjoining each other, and are located in a central area of ​​the lifting mast between the two vertical inner mast profiles. The central area of ​​the lifting mast is preferably a central area that is arranged in the middle in the transverse direction of the lifting mast. In the lifting mast according to the invention, both the mast lift cylinder and the free lift cylinder are protected between the two vertical inner mast profiles of the inner mast, so that no additional protective devices are required to protect the mast lift cylinder from mechanical damage during operation of the double-stacker.Furthermore, the lifting mast according to the invention is provided with only two lifting cylinders, one for the mast lift and one for the free lift. This results in reduced construction effort and lower oil consumption from the two lifting cylinders, thus requiring a smaller oil tank for the hydraulic pump unit in the double-stacker. The smaller oil tank reduces the required installation space in the double-stacker, thereby reducing the vehicle's external dimensions in terms of width and / or length.

[0008] According to an advantageous embodiment of the invention, the two outer mast profiles of the outer mast are connected to each other by means of a lower outer mast crossbeam and an upper outer mast crossbeam, and the two inner mast profiles of the inner mast are connected to each other by means of a lower inner mast crossbeam and an upper inner mast crossbeam, wherein the mast lifting cylinder is connected to the lower outer mast crossbeam and to the upper inner mast crossbeam. With such a connection of the mast lifting cylinder, which is arranged in the central region of the lifting mast between the two vertical inner mast profiles, to the lower outer mast crossbeam and the upper inner mast crossbeam, the mast lift can be achieved in a simple manner, with which the inner mast is raised and lowered within the outer mast.

[0009] According to an advantageous embodiment of the invention, the mast lifting cylinder comprises a cylinder tube and a piston rod extendable within the cylinder tube, wherein the cylinder tube of the mast lifting cylinder is connected to the lower outer mast crossbeam and the piston rod of the mast lifting cylinder is connected to the upper inner mast crossbeam. This allows for a simple arrangement of the mast lifting cylinder and results in minimal obstruction of view by the lifting mast when the piston rod of the mast lifting cylinder is extended upwards and the inner mast is raised.

[0010] According to an advantageous embodiment of the invention, the free-lift cylinder is connected to the lower inner mast crossbeam and to the load carriage by means of a traction element. This allows the free lift to be easily achieved with the free-lift cylinder, which raises the load carriage in the inner mast.

[0011] According to an advantageous embodiment of the invention, the free-lift cylinder comprises a cylinder tube and a piston rod extendable within the cylinder tube. A deflection pulley is rotatably arranged on the piston rod of the free-lift cylinder, over which the traction element is deflected. The axis of rotation of the deflection pulley relative to a longitudinal axis of the lifting mast, which runs in the longitudinal direction of the fork arms, forms an angle in the range of 20° to 35°, in particular an angle in the range of 25° to 30°. Such a rotated arrangement of the deflection pulley on the piston rod of the free-lift cylinder results in a small installation space requirement for the deflection pulley in the longitudinal direction of the lifting mast. This allows the lifting mast to be designed with compact dimensions in the longitudinal direction, thereby reducing the overall length of the double-stacker pallet truck.Such a rotated arrangement of the deflection pulley on the piston rod of the free-lift cylinder further offers the advantage that the section of the traction element guided from the deflection pulley to the load carriage can be arranged within the width of the cylinder tube of the mast lift cylinder, thereby keeping the distance between the free-lift cylinder and the mast lift cylinder in the transverse direction of the lifting mast small, or allowing the free-lift cylinder and the mast lift cylinder to be arranged overlapping in the transverse direction of the lifting mast, thus achieving minimal obstruction of view by the lifting mast.

[0012] According to an advantageous embodiment of the invention, a hydraulic connection line is connected to the cylinder tube of the mast lifting cylinder, and a hydraulic connecting line is routed from the piston rod of the mast lifting cylinder to the cylinder tube of the free-lift cylinder. This results in reduced construction effort for connecting the two lifting cylinders to a hydraulic pump unit and a control valve unit, since only a single hydraulic connection line needs to be routed to the cylinder tube of the mast lifting cylinder. The free-lift cylinder is preferably supplied with oil via a hollow piston rod of the mast lifting cylinder and the hydraulic connecting line.

[0013] According to an advantageous embodiment of the invention, the load carriage has a vertical load backrest which is arranged to be raised and lowered by means of guide rollers in the two inner mast profiles of the inner mast, wherein the load backrest is arranged between the two inner mast profiles of the inner mast. This results in a space-saving arrangement of the vertical load backrest, which allows the lifting mast to be designed with compact dimensions in the longitudinal direction, thereby reducing the external dimensions of the double-stacker pallet truck in terms of vehicle length.

[0014] According to an advantageous embodiment of the invention, the load back – viewed in the direction of the longitudinal axis of the lifting mast – is at least partially within the

[0015] The load-bearing back of the load carriage is thus arranged at least partially within the longitudinal extent of the inner mast profiles in the longitudinal direction of the lifting mast and is therefore installed between the two inner mast profiles, which allows the lifting mast to be designed with compact dimensions in the longitudinal direction.

[0016] According to an advantageous embodiment of the invention, the outer mast profiles each have a C-shaped cross-section with a cross web near the load and a cross web farther from the load, wherein the two outer mast profiles of the outer mast are arranged so that the cross webs point towards each other. This results in small dimensions of the outer mast profiles in the transverse direction of the lifting mast, which on the one hand minimizes obstructions to the operator's view of the lifting mast and on the other hand reduces the overall width of the double-stacker pallet truck.

[0017] According to an advantageous embodiment of the invention, the inner mast profiles each have a double-T profile cross-section, and the inner mast profile is nested within the outer mast profile. A load-adjacent cross web of the inner mast profile is positioned in front of the load-adjacent front face of the load-adjacent cross web of the outer mast profile, and a load-remote cross web of the inner mast profile is positioned between the load-adjacent and load-remote cross webs of the outer mast profile. With this arrangement of the inner mast profiles, compact dimensions of the lifting mast are achieved in both the longitudinal and transverse directions, thereby reducing the external dimensions of the double-stacker truck in terms of both length and width.

[0018] The invention further relates to a forklift truck, in particular a double-stacker, with a lifting mast according to the invention.

[0019] The industrial truck has the same advantages already mentioned in connection with the lifting mast.

[0020] The invention has a number of advantages.

[0021] The lifting mast according to the invention features a cost-effective design with minimal material usage and low manufacturing costs, as well as compactness in both the longitudinal and transverse directions. The lifting mast comprises only two lifting cylinders, which are protected from damage within the mast and require a small oil volume for operation. The lifting mast according to the invention easily fulfills the requirements for a lifting mast of a double-stacker pallet truck.

[0022] The lifting mast according to the invention has improved compactness and improved visibility through the lifting mast due to the outer mast profiles with a C-shaped cross-section, the load carriage installed or integrated between the two inner mast profiles, and the lifting cylinders (mast lifting cylinder, free lifting cylinder) arranged in the central area of ​​the lifting mast.

[0023] The compactness with small dimensions in the longitudinal direction of the lifting mast is achieved by integrating the free lift cylinder and the mast lift cylinder into the central area of ​​the lifting mast, as well as by arranging the load back of the load carriage between the two inner mast profiles of the inner mast.

[0024] The outer mast profiles with their C-shaped cross-section and the inner mast profiles with their double-T profile cross-section enable a compact design along the length of the lifting mast. Even with a fork width of up to 560 mm for the two fork arms, there is still room for a load carriage integrated between the two inner mast profiles. Combined with only two lifting cylinders (mast lift cylinder and free lift cylinder) in the center of the lifting mast, this results in minimal obstruction of the operator's view, which offers advantages for safe operation of a double-stacker pallet truck.

[0025] The lifting mast according to the invention makes it possible to provide a double-stacker with small dimensions in the longitudinal direction as well as in the transverse direction of the vehicle, thereby optimizing the loading and unloading activity of the double-stacker, increasing the maneuverability of the double-stacker and optimizing the warehouse occupancy.

[0026] The lifting mast according to the invention has only two lifting cylinders (mast lifting cylinder, free lifting cylinder), which, due to the reduced oil requirement, allows the volume of the oil tank and thus its installation space requirement in the double-stacker to be reduced.

[0027] Further advantages and details of the invention are explained in more detail by way of example using the embodiment shown in the schematic figures. Figure 1 shows a side view of a double-stacker pallet truck, Figure 2 shows a top view of the lifting mast of the Figure 1 in a representation according to arrow A, Figure 3 a front view of the lifting mast of the Figure 1 in a representation according to arrow B, Figure 4, a perspective view of the lifting mast of the Figure 3 with the load carriage lowered, Figure 5 the lifting mast of the Figure 4 with the load carriage raised in free lift and Figure 6 the lifting mast of the Figures 4 and 5with the inner mast raised during the mast lift.

[0028] In the Figure 1 Figure 1a shows a side view of a forklift truck 1 designed as a double-stacker high-lift truck 1.

[0029] The double-stacker pallet truck 1 has a drive unit 2 and a load unit 3.

[0030] In the drive section 2 a steerable drive wheel 5 is arranged, with which the double-stacker truck 1 supports itself on a roadway.

[0031] The load section 3 comprises two load arms 6a, 6b spaced apart in the transverse direction of the vehicle, each with a load roller assembly 7 at its tip, which supports the double-stacker 1 on the roadway. The load section 3 can be raised and lowered relative to the drive section 2 by means of an initial lifting device 8.

[0032] A lifting mast 10 is arranged on the load section 3, which is equipped with a load carriage 11 comprising two fork arms 12a, 12b spaced apart in the transverse direction Q of the lifting mast 10 and thus in the transverse direction of the vehicle. The load carriage 11 with the fork arms 12a, 12b can be raised and lowered relative to the load arms 6a, 6b, so that a first load carrier, for example a pallet, can be handled with the load arms 6a, 6b, and a second load carrier, for example a pallet, can be handled with the fork arms 12a, 12b.

[0033] The lifting mast 10 of the double-decker industrial truck 1 is in the Figures 2 to 6 A more detailed explanation.

[0034] The lifting mast 10 has an outer mast 15 designed as a stationary mast and an inner mast 16 arranged in the outer mast 15 so as to be raised and lowered. The load carriage 11, which is equipped with the two fork arms 12a, 12b, is arranged in the inner mast 16 so as to be raised and lowered.

[0035] In the Figures 1 to 3 The longitudinal axis L of the lifting mast 10, which runs in the longitudinal direction of the fork arms 12a, 12b, a transverse direction Q of the lifting mast 10 and the vertical direction V, along which the fork arms 12a, 12b can be raised and lowered, is further illustrated.

[0036] The outer mast 15 is formed by two vertical outer mast profiles 15a, 15b arranged laterally, in the transverse direction Q of the lifting mast 10. The inner mast 16 is formed by two vertical inner mast profiles 16a, 16b arranged laterally, in the transverse direction Q of the lifting mast 10.

[0037] The two vertical outer mast profiles 15a, 15b of the outer mast 15 are connected to each other by means of a lower outer mast crossbeam 15c, which runs in the transverse direction Q of the lifting mast 10, and an upper outer mast crossbeam 15d, which runs in the transverse direction Q of the lifting mast 10.

[0038] The two inner mast profiles 16a, 16b of the inner mast 16 are connected to each other by means of a lower inner mast crossbeam 16c, which runs in the transverse direction Q of the lifting mast 10, and an upper inner mast crossbeam 16d, which also runs in the transverse direction Q of the lifting mast 10. The two inner mast profiles 16a, 16b of the inner mast 16 are connected to each other by means of a further inner mast crossbeam 16e, which runs in the transverse direction Q of the lifting mast 10 and is arranged in the vertical direction V between the lower inner mast crossbeam 16c and the upper inner mast crossbeam 16d.

[0039] A mast lifting cylinder device 20 is provided for raising and lowering the inner mast 16 in the outer mast 15.

[0040] A free-lift cylinder device 21 is provided for raising and lowering the load carriage 11 in the inner mast 16.

[0041] In the lifting mast 10 according to the invention, the mast lifting cylinder assembly 20 comprises a single mast lifting cylinder 20a and the free lifting cylinder assembly 21 comprises a single free lifting cylinder 21a.

[0042] The mast lifting cylinder 20a and the free lifting cylinder 21a are arranged side by side, i.e. in the transverse direction Q of the lifting mast 10, and are located in a central area MB of the lifting mast 10 between the two vertical inner mast profiles 16a, 16b.

[0043] The central area MB of the lifting mast 10 is formed by a central area of ​​the lifting mast 10, which is arranged in the transverse direction Q of the lifting mast 10 centrally between the two vertical inner mast profiles 16a, 16b of the inner mast 16.

[0044] The mast lifting cylinder 20a is connected to the lower outer mast crossbeam 15c and to the upper inner mast crossbeam 16d. The mast lifting cylinder 20a has a cylinder tube 20b and a piston rod 20c arranged to extend vertically within the cylinder tube 20b. The cylinder tube 20b of the mast lifting cylinder 20a is attached to the lower outer mast crossbeam 15c by means of a bracket 25. The piston rod 20c of the mast lifting cylinder 20a is attached to the upper inner mast crossbeam 16d by means of a bracket 26.

[0045] The free-lift cylinder 21a is connected to the lower inner mast crossbeam 16c and is connected to the load carriage 11 by means of a traction element 30.

[0046] The free-lift cylinder 21a has a cylinder tube 21b and a piston rod 21c arranged vertically extendable in the cylinder tube 21b, on which a deflecting roller 31 is rotatably arranged, over which the traction element 30 is deflected.

[0047] The cylinder tube 21b of the free-lift cylinder 21a is attached to the lower inner mast crossbeam 16c of the inner mast 16 by means of a holder 27. The cylinder tube 21b of the free-lift cylinder 21a can also be attached to the further inner mast crossbeam 16e of the inner mast 16.

[0048] The traction element 30 is attached at a first end to the inner mast 16, in the illustrated embodiment to the further inner mast crossbeam 16e, guided over the deflection pulley 31 and deflected there, and at the second end attached to the load carriage 11.

[0049] The axis of rotation DA of the deflection pulley 31 forms an angle α with the longitudinal axis L of the lifting mast 10 in the range of 20° to 35°, preferably an angle in the range of 25° to 30°. In the illustrated embodiment, the intersection of the axis of rotation DA of the deflection pulley 31 with the longitudinal axis L of the lifting mast 10 is located on the side of the lifting mast 10 facing away from the load.

[0050] To supply hydraulic oil to the mast lift cylinder 20a and the free lift cylinder 21a, a hydraulic connection line 35 is connected to the cylinder tube 20b of the mast lift cylinder 20a, and a hydraulic connecting line 36 is led from the piston rod 20c of the mast lift cylinder 20a to the cylinder tube 21b of the free lift cylinder 21a. The hydraulic oil can flow through the hollow piston rod 20c of the mast lift cylinder 20a from the hydraulic connection line 35 to the hydraulic connecting line 36 and into the free lift cylinder 21a.

[0051] The load carriage 11 has a vertical load back 11a, which runs in the transverse direction Q of the lifting mast 10 and to which the two fork arms 12a, 12b are attached.

[0052] The load back 11a is arranged to be raised and lowered by means of guide rollers 40a, 40b in the two inner mast profiles 16a, 16b of the inner mast 16.

[0053] The load-bearing back 11a of the load-bearing sled 11 is - as in the Figure 2 As can be seen, the load back 11a is arranged in the transverse direction Q of the lifting mast 10 between the two inner mast profiles 16a, 16b of the inner mast 16. The load back 11a is positioned with its outer lateral edges AK within the inner edges IK of the two inner mast profiles 16a, 16b.

[0054] The load-bearing back 11a is arranged – viewed in the longitudinal direction L, i.e., in the direction of the longitudinal axis L, of the lifting mast 10 – at least partially within the longitudinal extent of the inner mast profiles 16a, 16b, i.e., within the extent of the inner mast profiles 16a, 16b in the longitudinal direction L of the lifting mast 10. This results in a compact dimension X3 of the lifting mast 10 in the longitudinal direction L of the lifting mast 10.

[0055] The outer mast profiles 15a, 15b each have a C-shaped cross-section with a transverse web 50a extending in the transverse direction Q of the lifting mast 10, located near the load, and a transverse web 50b extending in the transverse direction Q of the lifting mast 10, located further away from the load. The two outer mast profiles 15a, 15b of the outer mast 15 are arranged so that their transverse webs 50a, 50b are facing each other. Each outer mast profile 15a, 15b has a longitudinal web 50c extending in the longitudinal direction L of the lifting mast 10, to which the transverse webs 50a, 50b are integrally formed. The longitudinal webs 50c form flat outer surfaces of the lifting mast 10.

[0056] The inner mast profiles 16a, 16b each have a double-T profile cross-section and are nested within the associated outer mast profile 15a, 15b.

[0057] The inner mast profiles 16a, 16b each have a load-proximity cross web 55a extending in the transverse direction Q of the lifting mast 10 and a load-remote cross web 55b extending in the transverse direction Q of the lifting mast 10, wherein the load-proximity cross web 55a of the inner mast profile 16a or 16b is arranged in front of the load-proximity front face of the load-proximity cross web 50a of the outer mast profile 15a or 15b and the load-remote cross web 55b of the inner mast profile 15a or 15b is arranged between the load-proximity cross web 50a and the load-remote cross web 50b of the outer mast profile 16a or 16b.

[0058] The load-bearing back 11a of the load-bearing sled 11 is - as in the Figure 2As can be seen, in the transverse direction Q of the lifting mast 10 between the two inner mast profiles 16a, 16b of the inner mast 16, the load-adjacent cross webs 55a of the inner mast profiles 16a, 16b and the load back 11a are arranged in alignment with each other, so that the load back 11a and the load-adjacent cross webs 55a of the inner mast profiles 16a, 16b share the same installation space in the longitudinal direction L of the lifting mast 10.

[0059] The design of the outer mast profiles 16a, 16b with the C-shaped cross-section and the inner mast profiles 16a, 16b with the double-T profile cross-section, in conjunction with the profile nesting of the outer mast profiles 15a, 15b and inner mast profiles 16a, 16b, in conjunction with the arrangement of the single mast lifting cylinder 20a and the single free lifting cylinder 21a in the central area MB, makes it possible to provide sufficient installation space for the load back 11a of the load carriage 11 arranged between the inner mast profiles 16a, 16b, while maintaining compact dimensions of the lifting mast 10 in the transverse direction Q between the two inner mast profiles 16a, 16b, which allows for fork widths of the two fork arms 12a, 12b of up to 560 mm.

Claims

1. Lifting mast (10) for a forklift truck (1a), in particular a double-stacker (1), wherein the lifting mast (10) has an outer mast (15) designed as a stationary mast and an inner mast (16) arranged in the outer mast (15) so as to be raised and lowered, wherein a load carriage (11) provided with two fork arms (12a, 12b) is arranged in the inner mast (16) so as to be raised and lowered, wherein the outer mast (15) is formed by two laterally spaced vertical outer mast profiles (15a, 15b) and the inner mast (16) is formed by two laterally spaced vertical inner mast profiles (16a, 16b), wherein a mast lifting cylinder device (20) is provided which is designed to raise and lower the inner mast (16) in the outer mast (15), and a free lifting cylinder device (21) is provided is, which is trained to raise and lower the load carriage (11) in the inner mast (16), characterized by the fact thatthe mast lifting cylinder assembly (20) comprises a single mast lifting cylinder (20a) and the free lifting cylinder assembly (21) comprises a single free lifting cylinder (21a), wherein the mast lifting cylinder (20a) and the free lifting cylinder (21a) are arranged side by side in a central area (MB) of the lifting mast (10) between the two vertical inner mast profiles (16a, 16b).

2. Lifting mast (10) according to claim 1, characterized by the fact that the two outer mast profiles (15a, 15b) of the outer mast (15) are connected to each other by means of a lower outer mast crossbeam (15c) and an upper outer mast crossbeam (15d) and the two inner mast profiles (16a, 16b) of the inner mast (16) are connected to each other by means of a lower inner mast crossbeam (16c) and an upper inner mast crossbeam (16d), wherein the mast lifting cylinder (20a) is connected to the lower outer mast crossbeam (15c) and to the upper inner mast crossbeam (16d).

3. Lifting mast (10) according to claim 2, characterized by the fact thatthe mast lifting cylinder (20a) has a cylinder tube (20b) and a piston rod (20c) extendable in the cylinder tube (20b), wherein the cylinder tube (20b) of the mast lifting cylinder (20a) is connected to the lower outer mast crossbeam (15c) and the piston rod (20c) of the mast lifting cylinder (20a) is connected to the upper inner mast crossbeam (16d).

4. Lifting mast (10) according to claim 2 or 3, characterized by the fact that the free-lift cylinder (21a) is connected to the lower inner mast crossbeam (16c) and is connected to the load carriage (11) by means of a traction element (30).

5. Lifting mast (10) according to claim 4, characterized by the fact thatThe free-lift cylinder (21a) has a cylinder tube (21b) and a piston rod (21c) extendable in the cylinder tube (21b), wherein a deflection pulley (31) is rotatably arranged on the piston rod (21c) of the free-lift cylinder (21a), over which the traction element (30) is deflected, wherein an axis of rotation (DA) of the deflection pulley (31) forms an angle (α) of 20° with a longitudinal axis (L) of the lifting mast (10), which runs in the longitudinal direction of the fork arms (12a, 12b). 0 up to 35 0 , in particular an angle in the range of 25° 0 up to 30 0 , exhibits.

6. Lifting mast (10) according to one of claims 3 to 5, characterized by the fact that a hydraulic connection line (35) is connected to the cylinder tube (20b) of the mast lifting cylinder (20a) and a hydraulic connection line (36) is led from the piston rod (21c) of the mast lifting cylinder (20a) to the cylinder tube (21b) of the free lifting cylinder (21a).

7. Lifting mast (10) according to one of claims 1 to 6, characterized by the fact that the load carriage (11) has a vertical load back (11a) which is arranged to be raised and lowered by means of guide rollers (40a, 40b) in the two inner mast profiles (16a, 16b) of the inner mast (16), wherein the load back (11a) is arranged between the two inner mast profiles (16a, 16b) of the inner mast (16).

8. Lifting mast (10) according to claim 7, characterized by the fact that the load back (11a) - viewed in the direction of the longitudinal axis (L) of the lifting mast (10) - is arranged at least partially within the longitudinal extent of the inner mast profiles (16a, 16b).

9. Lifting mast (10) according to one of claims 1 to 8, characterized by the fact that the outer mast profiles (15a, 15b) each have a C-shaped cross-section with a load-adjacent cross web (50a) and a load-remote cross web (50b), wherein the two outer mast profiles (15a, 15b) of the outer mast (15) are arranged with the cross webs (50a, 50b) facing each other.

10. Lifting mast (10) according to claim 9, characterized by the fact thatthe inner mast profiles (16a, 16b) each have a double-T profile cross-section and the inner mast profile (16a; 16b) is nested in the outer mast profile (15a; 15b), wherein a load-adjacent cross web (55a) of the inner mast profile (16a, 16b) is arranged in front of a load-adjacent front face of the load-adjacent cross web (50a) of the outer mast profile (15a, 15b) and a load-remote cross web (55b) of the inner mast profile (16a; 16b) is arranged between the load-adjacent cross web (50a) and the load-remote cross web (50b) of the outer mast profile (15a; 15b).

11. Industrial truck (1a), in particular double-stacker (1a), with a lifting mast (10) according to one of the preceding claims.

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